为什么兰特（）+兰特（）产生负数？ [英] Why does rand() + rand() produce negative numbers?

问题描述

我观察到兰特（）当一个循环中调用只是一次库函数，它几乎总是产生正数。

I observed that rand() library function when it is called just once within a loop, it almost always produces positive numbers.

for (i = 0; i < 100; i++) {
    printf("%d\n", rand());
}

但是，当我添加两个兰特（）通话，数字生成现在有更多的负数。

But when I add two rand() calls, the numbers generated now have more negative numbers.

for (i = 0; i < 100; i++) {
    printf("%d = %d\n", rand(), (rand() + rand()));
}

有人能解释我为什么在第二种情况中看到负数？

Can someone explain why I am seeing negative numbers in the second case?

PS：我的环路初始化前种子函数srand（时间（NULL））

PS: I initialize the seed before the loop as srand(time(NULL)).

推荐答案

兰特（）被定义为返回之间的整数 0 和 RAND_MAX 。

rand() is defined to return an integer between 0 and RAND_MAX.

rand() + rand()

可能溢出。你观察到的可能是href=\"https://en.wikipedia.org/wiki/Undefined_behavior\">不确定的行为通过整数溢出引起

could overflow. What you observe is likely a result of undefined behaviour caused by integer overflow.

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